FR2795807A1 - DEVICE FOR LIMITING THE PROPAGATION OF A DEFORMATION IN A DOUBLE WALL TUBE - Google Patents

Abstract

The invention concerns a device limiting propagation of deformation in a wound double-walled tube (1). Said device comprises an outer wall (3) having a specific external diameter (D) and arranged around the inner wall (2), an annular space (5) being provided between said outer and inner walls. The device is characterised in that it consists in providing predetermined zones (7) in said annular space (5), each predetermined zone (7) being delimited between two sealing stop elements (9) whereof the radially opposite surfaces are in contact with the internal and external tubes; providing a hardenable compound (6) in each predetermined zone (7), the length (L) of each predetermined zone (7) being not less than 0.5 times the external diameter (D) of the outer shell (3).

Description

<I> Device for limiting the propagation of a deformation in a double-walled </I> <I> tube </I> The present invention relates to a device for limiting or stopping the propagation of a deformation in a double-walled tube windable on a reel and more particularly in a rigid tube used for the transport of fluids such as hydrocarbons.

The laying of a rigid tube or pipe on a seabed is most often carried out from a so-called laying ship. The laying is said to be in S when the tube affects the shape of an S between the laying vessel and the seabed and it is said in J when the tube affects the shape of a J. In the latter case, a ramp of guidance is provided on the laying vessel, which ramp can sometimes be partially submerged in water.

The rigid tube to be laid is stored on the laying vessel either in tube sections of given length but relatively short, the tube sections being connected together as the installation takes place, or wound in great length on a reel, the tube then being unwound from said coil during the laying operation. These laying operations are described in the API (American Petroleum Institute) Recommended Practice 17 A document of 1987.

When the tube has left the vessel and during the installation of said tube, it is important that the latter does not undergo plastic deformation in bending which would cause an ovalization of the tube, which ovalization causing a "weak singular point" which would favor initiation a collapse. Furthermore, when the tube is laid on a seabed at significant depths of water (typically greater than 300 m and up to 2000 m and more), the hydrostatic pressure exerted on the tube may be sufficient to initiate a deformation which tends to spread along the tube, in both directions. Of course, the formation of the deformation will be done, in priority on a "weak singular point" when it exists on the tube. When the deformation occurs, it is then necessary to replace at least the section or part of the tube comprising the deformed or crushed area. To avoid the propagation of the local deformation (s), it has been proposed to equip the tube with certain devices or organs, called deformation limiters ("buckle arrestor" in English).

Such deformation limiters are described in US Pat. Nos. 2,425,800, 3,747,356, 3,768,269 and 4,364,692.

In US 3,747,356, the method consists in connecting a cylinder to a cable, housing the cylinder inside a section of tube and then unwinding the tube and the cable at the same time, so as to keep the cylinder in the tube section during installation of the latter until the tube comes into contact with the seabed. Then we reassemble the cylinder to accommodate it in another section of tube to be laid and which is connected to the previous one. As a result, any deformation likely to occur, during the laying of the tube, between the laying vessel and the seabed is immediately stopped and is therefore not authorized to propagate along the sections of the tube. However, such a proposal does not present any solution or effectiveness to stop the deformations likely to propagate after the final installation of the tube on the seabed.

In US 3,768,269, it is proposed to locally increase the rigidity of the tube by having, at regular intervals for example at intervals between 100 m and 500 m, reinforcement rings whose length is between lm and 2, 5 m. Such a solution is only valid for tubes laid in sections because the reinforcing rings can be mounted and fixed in the factory on the tube sections, then transported by the laying vessel to the place of installation. When the tube is very long and wound on a storage reel, it then becomes practically impossible to wind the tube with its reinforcing rings on a reel because they would induce straight or substantially straight and non-deformable parts in the winding of the tube on the storage reel. To overcome this difficulty, it is possible to envisage mounting and fixing the reinforcement rings during the laying operations. But then this would require interrupting the installation, at regular intervals, in order to mount and fix the reinforcement rings.

To allow the winding of the tube on a reel, US 4,364,692 proposes to wrap a rod around the tube, in a tight manner, so as to form a certain number of turns which can be welded by their ends to the rod itself. same and / or tube.

According to another embodiment, the turns can be individual by welding the two ends and spacing them regularly on the part of the tube to be reinforced. As long as the tube is simple, increasing the diameter in the reinforced parts may be acceptable. But, when the tube is of the double jacket type ("pipe in pipe" in English), that is to say comprising an internal tube ("liner pipe" in English) which is threaded on the internal tube, the increase the diameter of the outer tube is unacceptable for the transport and storage of long lengths of double jacket tubes.

When the rigid tube to be laid is manufactured very long on land and then wound on a reel on the laying vessel, the solutions recommended in the documents cited above are not suitable because they use either long reinforcement rings, on the order of 1 to 2.5 m, as in US 3,768,209, or a winding of a reinforcing rod around the rigid tube as in US 4,364,692.

Another propagation limiter is described in US 3,860,039 and it consists in placing a sleeve over a rigid tube so as to have a constant outside diameter with a coating. The annular between the sleeve and the tube is filled with tar which transfers the crushing force to the sleeve.

Other end plugging systems ("bulkheads" in English) of rigid double-walled tube exist and are described in particular in WO 96/36831 and WO 98/17940. Such end plugs are not comparable to propagation limiters because the material in which they are made is not able to transfer the stresses applied to the outer tube on the inner tube.

The object of the present invention is to propose a method for making a propagation limiter for a deformation of a double-walled pipe or tube which can be wound up on a reel (reel in English) placed on a laying ship or equivalent system such as '' a barge, floating platform, etc ...

The subject of the present invention is a method for producing a limiter for the propagation of a deformation in a rigid tube comprising an external envelope having a determined external diameter and disposed around an internal envelope, an annular space being formed between said external envelopes and inner, and which is characterized in that it consists in providing predetermined zones in said annular space, each predetermined zone being delimited between two sealing stops whose radially opposite faces are in contact with the outer and inner tubes, to be disposed a compound curable in each predetermined zone, the length of each predetermined zone being at least equal to 0.5 times the external diameter of the outer envelope.

An advantage of the present invention is that the curable compound can be introduced into the annular space of the rigid grounded tube and cured because the length of each predetermined area which is filled with the cured compound is short enough to allow the winding of the rigid tube on a reel for example. The length dimension is considered to be axial, i.e. in the longitudinal direction of the rigid tube, as opposed to the radial dimensions, as the spacing between the outer wall of the inner casing and the inner wall of the external envelope, said spacing defining the annular space formed between said internal and external envelopes.

Depending on the nature of the curable compound used, single-component or two-component, the curing time can be long or short as required. It is possible to select a resin and hardener which are such that the hardening of the curable compound is completed in a predetermined area before the introduction of the same compound into another predetermined area.

Another advantage is that the limitation of propagation of a deformation is very simple to produce and does not require significant resources and that the curable compounds capable of being used are numerous enough to make the best choice which depends in particular on the duration of desired hardening.

Another advantage is that the number of determined zones filled with curable compound can be relatively large without creating any discomfort in the winding of the rigid tube on the receiving coil (s). Another advantage is that the curable compound constitutes, by its nature, good thermal insulation in the predetermined areas.

According to another characteristic of the invention, the sealing stops each consist of a radially deformable material which can be constituted, in one embodiment, by a set of elements that can be deformed individually in the radial direction, each element being able, by example, present the shape of a washer or a chevron.

Another advantage is that the at least radial deformation of each sealing stop makes it possible to adapt to the various local irregularities of the internal wall of the external envelope and therefore to the manufacturing tolerances of the external envelope.

According to another characteristic of the invention, the sealing stops are supported by one of their lateral faces on a support plate which is, for example, welded to the external wall of the internal envelope, a gap being provided between the free edge of the support plate and the internal wall of the outer casing. Therefore, after installation of the sealing stops, introduction of the hardenable compound between two consecutive bearing plates which thus delimit a predetermined area filled with the hardenable compound, then radial deformation of the sealing stops, there is also produced a watertightness or other liquid if it or this were to enter the annular space. Indeed, the curable compound after hardening fills said gap by relying on the expanded stops.

Other advantages and characteristics will appear more clearly on reading the description of several embodiments of the invention, as well as the appended drawings in which - Figure 1 is a sectional view of part of a rigid section double jacket; - Figure 2 is a schematic view of the assembly of sections of the rigid tube with two welds; - Figure 3 is another schematic view of the assembly of sections of the rigid tube with four welds. The rigid double-walled tube 1 with a longitudinal axis A, shown partially in FIG. 1, includes an internal envelope ("flow pipe" in English) or internal tube 2, the diameter and nature of the material being chosen as a function of the fluid. circulating in said inner tube, in particular as a function of the temperature and the pressure of said fluid, and an outer casing or outer tube 3 ("carrier pipe" in English) which is threaded onto the inner tube 2. The outer tube 3 generally has an outer diameter D which is oversized with respect to the inner tube 2 to allow the installation of a thermal insulator in the annular space 5 and represents a thickness which makes it possible to resist the hydrostatic pressure which is exerted on said outer tube 3. The rigid tube 1 generally comprises spacers or spacers, not shown, ("spacers" in English) which are integral with the external wall 4 of the t ube interior 2 and which are housed in the annular space 5 formed between the exterior 3 and interior 2 tubes.

According to the invention, a curable compound 6 is placed in predetermined zones 7 of the rigid tube 1. Each predetermined zone 7 has a given axial length L, which is for example delimited by two sealing stops 9 which are each in sealed contact and clamped by their radially opposite faces 9 ', 9 "on the internal 3' and external 4 walls of the tubes 3 and 2 respectively. The axial length L of each predetermined zone 7, between two consecutive sealing stops, is at least equal at 0.5 times the outside diameter D of the outside tube 3 and it is preferably between 0.5 and twice said diameter D, when the compound is hardened on the ground and before winding on a reel of the laying ship. and tests carried out with various types of curable compounds 6 have shown that a length L comprised within the limits indicated above is satisfactory; preferably, the limit s upper is equal to once the diameter D. In fact, the length L also depends and in particular on the conditions of use of the rigid tube 1. It is obvious that when the rigid tube is of very great length, the predetermined zones 7 will be numerous . Likewise, when the conditions of use such as the depth of the sea between the laying vessel and the seabed is important, the number and length of the predetermined zones 7 should be defined, so as to avoid spreading deformation, if it occurs, even after the final installation of part of the rigid tube on the seabed.

In a preferred embodiment of the invention, each sealing stop 9 is made of one or more radially deformable materials as specified below. Radially deformable sealing stops 9 have several advantages. A first advantage is that they each have a radial dimension, between the opposite faces 9 'and 9 ", which is less than the inside diameter d of the outer tube 3, so that after deformation, the radially opposite faces 9' and 9 "are in tight and tight contact on the internal wall 3 'and the external wall 4. In addition, the tight contact on the internal wall 3' makes it possible to absorb any surface irregularities that said internal wall 3 ' and due in particular to the manufacturing tolerances of the outer tube 3.

Each stop 9 can be constituted by a set of individually deformable elements 10 which are arranged in the form of a stack in the axial direction A, or nested one inside the other, as for example when each element 10 is in the form a chevron 11, the point of the chevrons being directed in the direction A.

In another embodiment, also shown in FIG. 1, each stop 9 is supported, by one of its lateral faces 12, on a support plate 13 whose radial dimension or radius counted from the longitudinal axis A is less than the internal radius of the outer tube 3, so that a gap 1 is formed between the free edge 14 of the support plate 13 and the internal wall 3 'of the external tube 3, the internal radial face of each plate support 13 being welded to the outer wall 4 of the inner tube 2.

According to a first implementation of the method according to the invention shown in Figure 2, we take a section of inner tube 2 and we have the rightmost sealing stop and, if necessary, the support plates 13 as well that the various elements which must be housed in the annular 5 such as spacers, thermal insulation, etc ... Then, we thread a section of outer tube 3 on the inner tube 2 so that the area of the inner tube where the sealing stops are located is covered last, the outer tube section being threaded in the opposite direction so as not to damage the sealing stops.

In another step, the internal tubes of two sections of double-walled pipe are welded, then the outer tube section is dragged until contact with the other outer tube section and the two sections are welded. The welds of the inner and outer tubes are indicated by the references 16 and 15 respectively; a two-weld process is thus implemented.

In another step, the internal stop or the right-most stop is deformed radially in FIG. 1 and the other seal stop 9 furthest to the left is positioned; then introducing or injecting the curable compound in sufficient quantity in the predetermined area 7 and the leftmost sealing stop is radially deformed.

FIG. 3 represents a process with four welds. After having taken a section of internal tube 2 and welded two support plates 13, separated by a given distance, a section of external tube 3 is threaded which is shorter than the section of internal tube. By one end of the short outer tube section, an expandable stopper 9 is introduced which is then placed under axial pressure to produce a radial deformation and therefore a tight contact on the internal wall of the short tube section. The desired quantity of curable compound is then introduced, then the second stop 9 is introduced through the other end of the short tube section, and said second stop is deformed radially. The welding steps will consist in welding the inner tube section with two other sections, the two welds being materialized by the zones or intervals 18 and 19, then in welding the short section of outer tube with two other longer sections of outer tube. , the two welds being materialized by the references 20, 21.

In some cases, the curable compound may include air, which is undesirable due to the embrittlement of the deformation limiting device 1 which it can induce. It is possible to expel the air from the curable compound if no backing plates are used and if the curable compound is compressed using the stops 9, the air expelled during compression being evacuated through the gap or vent which exists between the upper face of at least one stop and the internal wall of the outer tube, while said stops are in the non-deformed rest state. After deformation, a complete seal is obtained even with water or another liquid which would enter the annular space.

Another implementation of the method according to the invention consists in providing, at the level of each predetermined zone 7, at least one orifice 22 through which the hardenable compound 6 is injected under pressure into the predetermined zone 7. After filling of the latter , the orifice (s) 22 are sealed off. Under these conditions, the curable compound 6, which is free of air, is introduced into the intervals I formed between the free edge 14 of the support plates 13 and the internal wall 3 'and comes into contact with the stops of sealing which are in the non-deformed state. After hardening of the curable compound, an excellent seal is also obtained against any foreign body, solid or fluid, which circulates in the annular space 5. Preferably, two orifices 22 and 22 'are provided in each predetermined zone 7, the orifice 22 being formed in the lower part and the orifice 22 'in the upper part. The curable compound is injected under pressure into the predetermined area 7 until a small portion projects beyond the radially opposite orifice 22 '. Then, the orifices 22 and 22 ′ are closed off after the predetermined zone 7 has been completely filled.

Although it is possible to use as a curable compound a single-component whose pot life is relatively long, it is preferable to use a two-component compound whose resin and hardener are mixed in a filling head before its introduction into the predetermined zones 7, the pot life of which, at room temperature, is a few minutes. Among the monocomponents, mention may be made of MS 703-25 from Engineering Materials Systems Inc. Among the two-component compounds which can be used, mention may be made, for example, of FARALDITE 2012 (AW 2104 / HW 2934) sold by the company CIBA GEIGY. The duration of hardening can be adjusted by acting on the injection temperature of the mixture in each predetermined zone 7.

Claims (10)

1. Method for producing a limiter for the propagation of a deformation in a rigid tube (1) comprising an external envelope (3) having a determined external diameter (D) and arranged around an internal envelope (2), an annular space (5) being formed between said outer (3) and inner (2) envelopes, characterized in that it consists in providing predetermined zones (7) in said annular space (5), each predetermined zone (7) being delimited between two sealing stops (9), the radially opposite faces of which are in contact with the outer (3) and inner (2) tubes, to have a hardenable compound (6) in each predetermined area (7), the length (L) of each predetermined zone (7) being at least equal to 0.5 times the external diameter (D) of the external envelope (3). 2. Method according to claim 1, characterized in that the hardenable compound (6) is introduced and hardened before a winding of said rigid tube (1). 3. Method according to claim 2, characterized in that the length (L) of each predetermined area (7) is between 0.5 and 2 times the external diameter (D) of the outer envelope (3). 4. Method according to claim 1, characterized in that the sealing stops (9) each consist of a radially deformable material. 5. Method according to claim 4, characterized in that each sealing stop (9) is supported by at least one lateral side on a rigid support plate (13). 6. Method according to claim 7, characterized in that the support plate (13) has a radial dimension less than the radial dimension of the annular space (5). 7. Method according to claim 6, characterized in that the support plate (13) is metallic and made integral with the outer wall (4) of the inner casing (2), so as to provide a gap (I) between the free edge (14) of said support plate (13) and the inner wall (3 ') of the outer casing (3). 8. Method according to one of claims 2 to 5, characterized in that each sealing stop (9) of radially deformable material has a radial dimension less than the annular space (5) when it is introduced into said tube rigid, then it is subjected to a radial expansion to bring the radially opposite faces in close contact with the walls facing the outer and inner envelopes. 9. Method according to claim 1, characterized in that the curable compound (6) is an epoxy resin. 10. Method according to one of claims 1 to 3, or 9, characterized in that the curable compound (6) is injected into each predetermined area through at least one orifice (22) formed in the outer envelope (3) .